Photocatalytic and Photochemical Degradation of Liquid Waste Containing EDTA

The decontamination factor of liquid waste containing 60 Co is generally weak. This is due to the presence of complexant molecules. For instance, complexation of EDTA with 60 Co decreases efficiency of radioactive waste treatment. The aim of this study was to degrade EDTA in H2 O and CO2 and to concentrate free 60 Co in order to increase decontamination factor. A first test of radioactive waste treatment by photocatalysis was allowed to increase decontamination factor (60 Co) from 16 to 196 with a device requiring to be improved. The present work concerns the first step of the degradation process development with a more powerful device. These first experiments were leaded to follow the only EDTA oxidation. EDTA degradation was carried out by the following Advanced Oxidation Processes (AOP): UV/H2 O2 (photochemistry); UV/TiO2 (photocatalysis); UV/TiO2 /H2 O2 . A specific reactor was achieved for this study. The wavelength used was 254 nm (UVC). The photocatalytic degradation of EDTA was carried out with Degussa P-25 titanium dioxide (TiO2 ), which is a semiconductor photocatalyst. The degradation degree of EDTA and the intermediate products were monitored by TOC and ionic chromatography methods. The effects of various parameters such as pH and the quantity of H2 O2 were studied. This allows us to conclude that basic pH slows down EDTA degradation. The study showed that UV/H2 O2 process was the most effective treatment process under acid conditions. The rate of EDTA degradation was very high and reached 95% in 120 minutes. The presence of glyoxilic, oxalic, glycolic and formic acids was detected as degradation products. Among the intermediates produced by photochemistry, NO3 − ions presence informed of the amine degradations. These results highlighted faster EDTA degradation by photochemistry than photocatalysis.Copyright © 2011 by ASME